Skip to main content

Reset your password

Please enter the e-mail address you used to register to reset your password

Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact customerservices@ioppublishing.org

Registration complete

Thank you for registering with Physics World
If you'd like to change your details at any time, please visit My account

Close
Home » Page 1485

The future’s bright for DESY

How do you convert a major particle physics lab into a leading centre for materials science, chemistry and biology? That was the leading question confronting Helmut Dosch when he was appointed director of DESY in 2009 – the first condensed-matter physicist ever to hold that post.

In this exclusive video interview, Dosch explains why DESY, which is located in Hamburg, Germany, is making the transition from colliding particles to developing world-class “photon science” facilities that are used by scientists across a wide range of disciplines.

We will have a high-speed camera for the nanoworld 

Helmut Dosch, director of DESY

Dosch talks about the key role that the lab is playing in building the €1.2 billion European X-ray Free Electron Laser (XFEL), which Dosch describes as “a high-speed camera for the nanoworld”. At the heart of the laser is an electron accelerator that will run 3.4 km from DESY to an experimental hall on the outskirts of Hamburg.

The European XFEL uses superconducting cavity technology that was developed at DESY – and the same technology is now being used in preliminary designs for the International Linear Collider (ILC). The ILC will be the next big thing in particle physics after CERN’s Large Hadron Collider, and Dosch explains how DESY’s involvement in the project will keep the lab at the cutting edge of accelerator technology.

While he admits that it’s unlikely that the ILC will be built in Hamburg, there are plenty of options for boosting DESY’s photon-science capability. One discussed by Dosch is the possible conversion of the dormant HERA accelerator ring into a light source.

In a separate interview filmed in the experimental hall of the FLASH free electron laser, DESY’s director of photon science, Edgar Weckert, explains how that facility is informing the development of the European XFEL.

Weckert explains how FLASH was used to make aluminium momentarily transparent to light and other photon-science highlights at the facility. Indeed, FLASH is so popular that DESY has to turn down most of the requests it gets from scientists for time on the instrument. An enviable problem that soon could be relieved with the building of FLASH II, according to Weckert.

  • For readers interested in finding out more about the research at DESY, Journal of Physics B: Atomic, Molecular and Optical Physics has just published a special issue entitled Intense X-ray Science: the First Five Years of FLASH. All papers in the issue are free to download until March 2011.

Shining a light on FLASH

As director of photon science at DESY, Edgar Weckert is responsible for an impressive array of scientific equipment, including the FLASH free electron laser.

In this interview filmed in FLASH’s vast experimental hall, Weckert describes some of the laser’s greatest accomplishments, including how it was used to make aluminium momentarily transparent to light. FLASH has become so popular with scientists that DESY has to turn down a significant number of beam-time requests. But photon scientists mustn’t despair, according to Weckert, because plans are well under way for FLASH II, which will double the capacity of the existing facility.

Weckert also explains how FLASH is informing the development of the European XFEL and gives an update on DESY’s PETRA III light source, which has been up and running for about a year.

  • For readers interested in finding out more about the research at DESY, Journal of Physics B: Atomic, Molecular and Optical Physics has just published a special issue entitled Intense X-ray Science: the First Five Years of FLASH. All papers in the issue are free to download until March 2011.

New videos shine a light on DESY

By Hamish Johnston

How do you convert a major particle physics lab into a leading centre for materials science, chemistry and biology?  That was the leading question confronting Helmut Dosch when he was appointed director of DESY in 2009 – the first condensed-matter physicist ever to hold that post.

In this exclusive video interview, Dosch explains why DESY, which is located in Hamburg, Germany, is making the transition from colliding particles to developing world-class “photon science” facilities that are used by scientists across a wide range of disciplines.

Dosch talks about the key role that the lab is playing in building the €1.2 billion European X-ray Free Electron Laser (XFEL), which Dosch describes as “a high-speed camera for the nanoworld”. At the heart of the laser is an electron accelerator that will run 3.4 km from DESY to an experimental hall on the outskirts of Hamburg.

The European XFEL uses superconducting cavity technology that was developed at DESY – and the same technology is now being used in preliminary designs for the International Linear Collider (ILC). The ILC will be the next big thing in particle physics after CERN’s Large Hadron Collider, and Dosch explains how DESY’s involvement in the project will keep the lab at the cutting edge of accelerator technology.

While he admits that it’s unlikely that the ILC will be built in Hamburg, there are plenty of options for boosting DESY’s photon-science capability. One discussed by Dosch is the possible conversion of the dormant HERA accelerator ring into a light source.

In a separate interview filmed in the experimental hall of the FLASH free electron laser, DESY’s director of photon science, Edgar Weckert, explains how that facility is informing the development of the European XFEL.

Weckert explains how FLASH was used to make aluminium momentarily transparent to light and other photon-science highlights at the facility. Indeed, FLASH is so popular that DESY has to turn down most of the requests it gets from scientists for time on the instrument. An enviable problem that soon could be relieved with the building of FLASH II, according to Weckert.

If you want to know more about the research at DESY, Journal of Physics B: Atomic, Molecular and Optical Physics has just published a special issue entitled Intense X-ray Science: the First Five Years of FLASH. All papers in the issue are free to download until March 2011.

Digesting Stephen Hawking's new book

grand design.jpg

By James Dacey

I’m a big fan of the Guardian‘s Digested Read in which columnist John Crace takes a newly released book and condenses it into short humorous parody of the original work, often relying on our intimate knowledge of the celebrity author in question. This week, it was the turn of Stephen Hawking and his recent release The Grand Design, which was making headlines across the globe before it was even released last week.

I have picked out a couple of bits that really made me chortle:

“Quantum theories can be formulated in many ways, but the most intuitive is the description of it as a system that has not just one history but every possible history. Let me explain. This book may look unique. But really it’s almost identical to at least three other books in which I have tried and failed to explain cutting-edge astrophysics to the scientifically illiterate…

“But I suppose we should start with Democritus’s theory of the atom, God, scientific determinism and effective theory because that’s pretty much what I’ve done in the past, but I can’t help feeling I’m wasting my time. Though that feeling may not be correct, as there are many different pictures of reality. In other words, there is no theory-independent concept of reality; rather there is only model-dependent realism, where our four-dimensional world may be shadows on the boundaries of 11-dimensional space–time. Sod it. I was right first time. I have lost you already. So there’s probably no point you reading the next bit about quarks and pi mesons.”

The parody is written in good spirit, but I couldn’t help but smile in recognition when I read Crace’s closing footnote: “Er…thanks Stephen, that’s lovely. If you could just end with something you haven’t written before to create a few headlines, then we’re done. How about God doesn’t exist? Lovely job. Let’s do it all again in a couple of years.”

Read the full digested read on the Guardian website.

Logic circuit takes the heat

Researchers in the US are the first to make tiny electromechanical logic circuits that operate at temperatures as high as 500 °C. The circuits contain two switches made from silicon carbide and operate as a logical NOT gate. The team believes that its nanoelectromechanical system (NEMS) could be used in microcontrollers embedded in hot machinery such as jet engines or oil-drilling rigs.

Modern technology is increasingly reliant on embedded computer control systems, but some equipment is simply far too hot for conventional silicon electronics to function. The problem is that normal computer chips do not work above about 300 °C because heat causes transistor junctions to degrade – and also because thermally excited electrons alter the electronic properties of the semiconductor.

Designers have got round this problem by making high-temperature microcontrollers from silicon carbide (SiC), which is much more resistant to heat damage than plain silicon. In addition, the amount of energy needed to thermally excite an electron is much greater in SiC. Unfortunately, transistors made from SiC tend to be large, slow and power hungry and only work at high voltages.

Switching cantilever

Now, Mehran Mehregany and colleagues at Case Western Reserve University in Cleveland, Ohio, have shown that superior high-temperature microcontrollers can be made from tiny mechanical switches just a few hundred nanometres in size.

To build its device, the team coated a silicon wafer with a thin layer of silicon oxide and then a 400 nm thick layer of SiC. The researchers then used electron beam lithography to make a simple switch comprising two SiC electrodes (the gate and drain) that are spanned by a SiC cantilever beam (the source). The SiC switch was released from the wafer by using a chemical to etch away the silicon oxide.

When a voltage was applied between the gate and source, the electrostatic force was found to pull the beam into contact with the drain (but not the gate). This allows current to flow between source and drain, making the device a NEMS field-effect transistor. Mehregany and colleagues were then able to make a NOT logic gate by combining two such switches.

The team operated the device at 500 °C at a frequency of 500 kHz and with logical input voltages of ±6 V. While this voltage is much higher than silicon logic devices – which work at 3 V or less – the NEMS logic of ±6 V is in line with other high-temperature devices, according to the team. And because the switching voltage is not an intrinsic property of the device – as it is in a semiconductor – the device’s voltage could in principle be further reduced by making the component switches smaller.

No lower limit

The team was able to operate a typical switch for about 21 billion cycles at room temperature before the cantilever beam fractured. At 500 °C, however, the switches only lasted about 2 billion cycles. The team also found that at this temperature, there was a tiny ball of SiC at one end of the fracture. This is puzzling because SiC normally sublimates at 1800 °C.

Case physicist Te-Hao Lee told physicsworld.com that the ball fracture could be caused by a temperature-related electrical spike that occurred during the switching operation. “By refining the design of the switch, it is possible to reduce the bending stress on the switch and as a result, improve the switch reliability and lifetime significantly,” he says.

Gigahertz operation

Lee believes that these and other improvements could result in devices that could deliver a trillion cycles of reliable operation at gigahertz speeds – which would exceed the speed and lifetime requirements of a typical microcontroller circuit.

In addition to boosting the performance of individual switches, the team is working on integrating the devices into more complex circuit elements such as an adder or register. It is also looking at the problem of how to package the devices for high-temperature applications.

The work is reported in Science 329 1316.

Chu’s right about bouncing atoms?

By Hamish Johnston

UPDATE: Chu and colleagues have uploaded a second preprint related to the gravitational redshift debate.

Steven Chu and Claude Cohen-Tannoudji shared the 1997 Nobel Prize for Physics (along with William Phillips) for their work on the laser cooling and trapping of atoms.

Now the two Nobel Laureates find themselves on opposing sides of a “preprint battle” over the re-interpretation of an experiment done in 1998. The experiment involved using vertical laser pulses to bounce atoms up and down in order to study the interference patterns that occur when different atomic trajectories meet.

In February 2010, Chu (who is now US energy secretary) along with Holger Mueller and Achim Peters published new calculations showing that the experiment confirms gravitational redshift to a few parts in a billion.

A result of Einstein’s general theory of relativity, gravitational redshift is the stretching of the wavelength of a particle as it moves away from a massive object such as the Earth. Other experiments have confirmed this aspect of general relativity to much greater precision, but these involved macroscopic objects. Any deviation in redshift for a quantum particle such as an atom could point towards a unified theory of gravity and quantum mechanics – the Holy Grail of physics.

But about 10 days ago, Cohen-Tannoudji and colleagues uploaded a paper to the arXiv preprint server in which they argue that Chu and colleagues have not measured gravitational redshift after all.

As far as I can tell, Cohen-Tannoudji and colleagues argue that Chu and company made a mistake in their calculation of the expected interference caused by a deviation from gravitational redshift. When the correct calculation is done, they say, a deviation from gravitational redshift has zero effect on what was measured in 1998.

Now, Chu and colleagues have hit back with their own preprint. It argues that Cohen-Tannoudji and team made their calculations using mathematics that assumes gravitational redshift cannot be violated – essentially precluding its violation!

Stay tuned for round three.

Searching the Sun for dark matter

Physicists have so far failed to find direct evidence for the existence of dark matter – the non-luminous substance believed to make up some 23% of the mass-energy content of the universe – at least to the satisfaction of everyone working in the field. But now physicists in Portugal and the UK suggest that such evidence could be found in precision measurements of the neutrinos given off by the Sun.

Although astronomical observations provide indirect evidence for dark matter, experiments on Earth have yet to secure direct and definitive proof that this form of matter exists. Ilidio Lopes of the Technical University of Lisbon and the University of Évora in Portugal together Joseph Silk of the University of Oxford argue that proof might lurk within the Sun. This is because the huge gravitational field of our star is expected to suck in weakly interacting massive particles (WIMPs), which are a leading candidate for dark matter.

Once trapped inside the core of the Sun, WIMPs should collide with protons, gain energy slightly and gradually remove heat outwards from the centre of the star. As such, the radial distribution of temperature across the Sun would be different in the absence or presence of dark matter.

Taking the Sun’s temperature

The pair’s plan for identifying this altered temperature distribution relies on detecting neutrinos that are generated by a number of different fusion reactions within the Sun. The crucial point is that different reactions take place at different distances from the centre of the Sun – the reaction producing boron-8, for example, takes place at just 4% of the solar radius whereas that involving the production of nitrogen-13 occurs at 16% of the solar radius. Since the strength of these reactions depends strongly on temperature, and this dependence varies from reaction to reaction, the presence of solar dark matter would lead to a well defined change in the relative fluxes of the neutrinos produced in the different reactions. The detection of dark matter would therefore fall to experiments set up to measure neutrino fluxes, with the fluxes from the different fusion reactions distinguishable on the basis of the distinctive energy spectra of the neutrinos in each case.

The two physicists used computer simulations to calculate, given certain assumptions about the properties of WIMPs – including their mass, strength of interaction with baryons, and likelihood of mutual annihilation – that the presence of dark matter could increase the flux of neutrinos produced in the boron-8 reactions by as much as 30% and would decrease the flux from the basic proton–proton reaction by around 2%. These results back up a similar analysis carried out earlier this year by Marco Taoso of the University of Valencia in Spain and colleagues, who used slightly different theoretical assumptions and computer codes.

Lopes and Silk say that if they are lucky and WIMPs do have the characteristics assumed in their analysis then the effect of dark matter on the strength of the relative neutrino fluxes would be striking enough to permit a direct detection of dark matter in upgrades to existing solar neutrino detectors. But they claim that their approach could in any case reduce the number of candidate dark-matter particles put forward by particle physicists and cosmologists.

Nothing in the data yet

Gianpaolo Bellini, spokesperson of the Borexino solar-neutrino detector at the Gran Sasso laboratory in Italy, points out that measurements by Borexino and other similar experiments are consistent with the current standard solar model, which does not take into account possible contributions from dark matter. He says that there is a significant margin of error on this agreement between measurements and model, potentially leaving room for some variation in neutrino flux along the lines laid out by Lopes and Silk. But he says he would need to see a more detailed presentation of their argument before really judging the feasibility of their approach.

Dave Wark of Imperial College in London describes the research as “extremely interesting” but agrees with Bellini that more information is needed to make a detailed critique. In particular, he says that further work is required to establish that any apparent solar cooling is due to dark matter rather than to misunderstandings of the Sun’s internal properties. He adds that changes to the parameters governing neutrino oscillation might also mimic or hide the effects of dark matter.

The work is described published online in Sciencexpress.

And the winner is…

astro image.jpg
The winning image of the 2010 astronomy photographer of the year award (Courtesy: Tom Lowe)

By Michael Banks

US photographer Tom Lowe has beaten hundreds of amateur and professional photographers from around the globe to win the 2010 astronomy photographer of the year award run by the Royal Observatory in Greenwich and Sky at Night Magazine.

Lowe’s winning shot, “Blazing Bristlecone”, which secured him the top prize of £1000, was taken on 14 August 2009 and shows the star-riddled Milky Way arching over an ancient bristlecone pine tree, which can live as long as 5000 years.

The photo was taken in White Mountains, California, with a Canon 5D Mark II camera and an exposure time of 32 seconds. “I like the way the tree follows the Milky Way and the definition is very good,” says astronomer Patrick Moore, one of the 10 panellists who judged the images.

The competition received over 400 entries from more than 25 countries and was split into three categories – Earth and space, our solar system, and deep space – together with young photographer award of the year, which was won by Dhruv Arvind Paranjpye, aged 14, from India. The winners of each category are here.

Selected images will be shown in a free exhibition at the Royal Observatory, which begins today and runs until February.

Peer review highly sensitive to poor refereeing, claim researchers

Just a small number of bad referees can significantly undermine the ability of the peer-review system to select the best scientific papers. That is according to a pair of complex systems researchers in Austria who have modelled an academic publishing system and showed that human foibles can have a dramatic effect on the quality of published science.

Scholarly peer review is the commonly accepted procedure for assessing the quality of research before it is published in academic journals. It relies on a community of experts within a narrow field of expertise to have both the knowledge and the time to provide comprehensive reviews of academic manuscripts.

While the concept of peer review is widely considered the most appropriate system for regulating scientific publications, it is not without its critics. Some feel that the system’s reliance on impartiality and the lack of remuneration for referees mean that in practice the process is not as open as it should be. This may be particularly apparent when referees are asked to review more controversial ideas that could damage their own standing within the community if they give their approval.

Questioning referee competence

Stefan Thurner and Rudolf Hanel at the Medical University of Vienna set out to make an assessment of how the peer-review system might respond to incompetent refereeing. “I wanted to know what would be the effects on peer review as a selection mechanism if referees were not all good, but behaved according to different interests,” Thurner told physicsworld.com.

The researchers created a model of a generic specialist field where referees, selected at random, can fall into one of five categories. There are the “correct” who accept the good papers and reject the bad. There are the “altruists” and the “misanthropists”, who accept or reject all papers respectively. Then there are the “rational”, who reject papers that might draw attention away from their own work. And finally, there are the “random” who are not qualified to judge the quality of a paper because of incompetence or lack of time.

I wanted to know what would be the effects on peer review as a selection mechanism if referees were not all good, but behaved according to different interests Stefan Thurner

Within this model community, the quality of scientists is assumed to follow a Gaussian distribution where each scientist produces one new paper every two time-units, the quality reflecting an author’s ability. At every step in the model, each new paper is passed to two referees chosen at random from the community, with self-review excluded, with a reviewer being allowed to either accept or reject the paper. The paper is published if both reviewers approve the paper, and rejected if they both do not like it. If the reviewers are divided, the paper gets accepted with a probability of 0.5.

Big impact on quality

After running the model with 1000 scientists over 500 time-steps, Thurner and Hanel find that even a small presence of rational or random referees can significantly reduce the quality of published papers. When just 10% of referees do not behave “correctly” the quality of accepted papers drops by one standard deviation. If the fractions of rational, random and correct referees are about 1/3 each, the quality selection aspect of peer review practically vanished altogether.

“Our message is clear: if it can not be guaranteed that the fraction of rational and random referees is confined to a very small number, the peer-review system will not perform much better than by accepting papers by throwing (an unbiased!) coin,” explain the researchers.

Daniel Kennefick, a cosmologist at the University of Arkansas with a special interest in sociology, believes that the study exposes the vulnerability of peer review when referees are not accountable for their decisions. “The system provides an opportunity for referees to try to avoid embarrassment for themselves, which is not the goal at all,” he says.

Kennefick feels that the current system also encourages scientists to publish findings that may not offer much of an advance. “Many authors are nowadays determined to achieve publication for publication’s sake, in an effort to secure an academic position and are not particularly swayed by the argument that it is in their own interests not to publish an incorrect article.”

Don’t forget the editors

But Tim Smith, senior publisher for New Journal of Physics at IOP Publishing, which also publishes physics world.com, feels that the study overlooks the role of journal editors. “Peer-review is certainly not flawless and alternatives to the current process will continue to be proposed. In relation to this study however, one shouldn’t ignore the role played by journal editors and Boards in accounting for potential conflicts of interest, and preserving the integrity of the referee selection and decision-making processes,” he says.

Michèle Lamont a sociologist at Harvard University who analyses peer review in her 2009 book, How Professors Think: Inside the Curious World of Academic Judgment, feels that we expect too much from peer review. Lamont believes that we should never hope for “uncorrupted” evaluation of new science as all researchers are embedded in social and psychological networks. She feels that one way to improve the system, however, is to make assessment criteria more relevant to specific disciplines.

When asked by physicsworld.com to offer an alternative to the current peer-review system, Thurner argues that science would benefit from the creation of a “market for scientific work”. He envisages a situation where journal editors and their “scouts” search preprint servers for the most innovative papers before approaching authors with an offer of publication. The best papers, he believes, would naturally be picked up by a number of editors leaving it up to authors to choose their journal. “Papers that no-one wants to publish remain on the server and are open to everyone – but without the ‘prestigious’ quality stamp of a journal,” Thurner explains.

This research is described in a paper submitted to the arXiv preprint server.

Nanostructure filter zaps bacteria

A water-purifying filter made from normal cotton coated in nanostructures has been developed by researchers at Stanford University in the US. They say that the device, which works by killing bacteria with electrical impulses, is 80,000 times faster than conventional filters and could become a useful tool for remote communities in the developing world. But the breakthrough has already been met with a degree of scepticism by other scientists in the field, who question elements of the design.

Instead of physically trapping bacteria like most existing filters do, the new filter lets them flow on through with the water. But by the time the harmful pathogens have passed into a water container they have been exposed to an electric field, generated by the coated cotton, which kills large swathes of them.

To develop their nano coating, Yi Cui and his Stanford colleagues built on recent work investigating the use of silver nanoparticles for antibacterial treatment of a variety of substrates, including cloth and medical devices. Instead of particles, however, Cui’s team use silver nanowires ranging from 40 to 90 nm and combine them with carbon nanotubes of similar dimensions, which are exceptionally strong and good electrical conductors.

“We got it at Wal-mart”

The nanowires and nanotubes are prepared separately and then added to simple dyes – the nanotubes in a water-based dye and the nanowires in an alcohol-based dye. The dyes are then applied to cotton, which was chosen as the foundation material because it is cheap as well as being relatively strong and chemically robust. “We got it at Wal-mart,” explains Cui. Adding, “The amount of silver used for the nanowires was so small that the cost was negligible.”

In lab tests, a piece if fabric comprising several layers of coated cotton was connected to an electrical power source set to 20 V. Then, water containing a common strain of E. Coli was poured onto the fabric and allowed to pass through at a rate of 10,000 L/h/m2. With this set up, the researchers found that they could rid the water of 98% of bacteria at a rate that was 80,000 times faster than was possible with existing filters.

“The technique is interesting because it uses widely available cotton fabric as the basis for the filter and it relies on an electric current rather than mesh size to remove the pathogen hazard,” says Andrew Scott, a director at Practical Action, a charity that promotes technology for development. Scott is concerned, however, that the filter requires a source of electricity, which is not always available in remote communities.

Energy troubles

The issue of energy requirements also troubles Mark Shannon, a water engineer at the University of Illinois in the US. “[The researchers] reported about 2 logs reduction of pathogens, which is a “modest” reduction – typically you want more than 4 logs,” he says. “So the amount of energy used to kill off the pathogens per unit volume of water is likely much greater than that for boiling water”.

The Stanford team acknowledge that further development is needed to improve the purification process. “With one filter, we can kill 98% of the bacteria,” says Cui. “For drinking water, you don’t want any live bacteria in the water, so we will have to use multiple filter stages.

“It will also be important to investigate how well the filter retains the nanomaterials we use, so that we can be sure the filtered water does not contain silver nanowires and carbon nanotubes,” he says.

Peter Dobson, an engineer scientist at the University of Oxford, agrees that the idea of an electrically controlled membrane is a “worthy and interesting idea” and he is impressed by the use of cotton as an inexpensive base material. However, he is frustrated by the lack of experimental detail in the related research paper. “The actual experimental set-up is very poorly described, and the manner in which the filter has been constructed is not clear, and it is also not clear how the electrical connections were made.

This research is described in a paper in Nano Letters.

Copyright © 2026 by IOP Publishing Ltd and individual contributors